Phase 3 study of fidaxomicin for clostridium difficile infection (CDI)

Optimer Pharmaceuticals announced positive top-line results from the second of two Phase 3 trials evaluating the safety and efficacy of fidaxomicin (OPT-80) in patients with Clostridium difficile Infection (CDI). This study was a multi-center, randomized, double-blind clinical trial, which enrolled 535 adult subjects conducted in approximately 100 clinical sites throughout North America and Europe. Subjects with confirmed CDI received either fidaxomicin (200 mg q12h) or Vancocin (125 mg q6h). The trial met the primary endpoint of non-inferiority with 91.7% of patients treated with fidaxomicin (per protocol population) achieving clinical cure vs. 90.6% for Vancocin, the only FDA-approved therapy for CDI. Fidaxomicin also had significantly lower recurrence rates and higher global cure rates (defined as cure with no recurrence within four weeks of completing therapy) compared to Vancocin. Only 12.8% of patients treated with fidaxomicin experienced a recurrence vs. 25.3% of patients treated with Vancocin (p = 0.002). Additionally, 79.6% of patients treated with fidaxomicin achieved a global cure versus 65.5% of patients treated with Vancocin (p < 0.001).

Fidaxomicin is the first in a new class of antibiotics called macrocycles, which inhibit the bacterial enzyme RNA polymerase, resulting in the death of C. difficile. The narrow-spectrum profile of fidaxomicin may eradicate C. difficile selectively with minimal disruption to the normal intestinal flora. Most broad-spectrum antibiotics, including metronidazole and vancomycin, disrupt these flora.

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